The present disclosure relates to the field of large-scale water treatment, and more particularly to the treatment of aqueous borne waste from municipal, commercial and industrial operations; but is not limited thereto. In patents: U.S. Pat. No. 5,762,418, U.S. Pat. No. 6,029,955, U.S. Pat. No. 6,036,357, U.S. Pat. No. 6,322,056, U.S. Pat. No. 6,554,259, U.S. Pat. No. 6,599,426, U.S. Pat. No. 6,926,437, and U.S. Pat. No. 7,083,324, the present inventor defines apparatus and methods for treating sludge and other materials. The present invention extends this body of knowledge and particularly utilizes the combination of gravity and buoyancy and automated inflation to buoyant elements to assist in mixing for improved efficiency in aerobic bacteria growth in waste digesters.